The rates of HIV/STI sexual risk behaviors among adolescents with substance use disorders (SUD) are significantly higher compared with youth without SUD, yet HIV/STI sexual risk reduction is not regularly implemented within adolescent SUD treatment programs; current state policies neither require providers in clinics delivering substance use treatment to offer HIV/STI sexual risk reduction nor offer providers tools or training for HIV/STI prevention. To address this urgent public health priority and the lack of efficacious family- based HIV/STI sexual risk reduction programs for youth with SUD in treatment, we propose to a) develop a manualized family-based sexual risk reduction intervention that builds the capacity of outpatient clinics to address adolescent sexuality more systematically, to promote youth safer sex practices, and to reduce youth HIV/STI sexual risk behaviors; and b) pilot test the intervention to examine the intervention's feasibility and acceptability within clinics and to determine key research parameters in preparation for a randomized controlled trial (RCT). The intervention development process will use a Community Based Participatory Research model of adaptation and development that has been successfully implemented by the PI in other settings. We will conduct formative work to guide adaptation of a multi-family group HIV/STI sexual risk reduction intervention that has demonstrated efficacy with youth (13-18 years), who have non-SUD psychiatric disorders (Project STYLE; R01MH63008; PI: Brown). This formative work will leverage the research sample of CASALEAP, an ongoing NIDA-funded, naturalistic study of the effectiveness of outpatient SUD treatment for adolescent (R01 DA019607; PI: Hogue). We will then pilot-test the resulting new manualized intervention (STYLEnS: STYLE and Substance) with a sample of male and female adolescents age 13-18 years (n=60) with SUD who are in treatment in mental health outpatient treatment programs. Pilot participants will be randomly assigned to either STYLEnS or an attention control intervention. Participants will receive a full-day group intervention on the day of randomization (multi-family, caregivers alone and adolescents alone), return in two weeks for an individual adolescent/caregiver dyad session, and participate in a half-day booster group session three months later. The pilot test will examine feasibility, acceptability, key study parameters, and range of possible effect sizes of implementing STYLEnS in outpatient clinics treating adolescents with SUD in preparation for a RCT. Acceptability and feasibility will be assessed using process measures following each session as well as after the intervention is completed. We will assess change in sexual risk behavior outcomes from baseline to 3 months post-intervention. Implementing a HIV/STI sexual risk reduction intervention in clinics providing SUD treatment represents an innovative approach to enable SUD treatment providers to address the heightened HIV/STI risk in SUD youth and responds to the need to provide sexual risk reduction intervention services for youth with SUD that can be easily disseminated to clinical settings.